Adhesives form a large part of daily activity for everyone, whether in the form of tape used to close a package or secure items together, bandages, envelopes, notepads, diaper tabs or any one of many other products in common use. The key requirements for adhesives are that they should have suitable cohesive and adhesive properties at end use conditions and during application, whether by solvent or bulk casting. Usually these adhesives are prepared from a mixture of resin, copolymer and a plasticizer to soften the adhesive and enhance tack.
Adhesives prepared from blends incorporating these polymers have very good adhesive and strength properties at room temperature and can be processed by conventional melt coating and extrusion techniques because of their good flow characteristics. Because of the excellent combination of properties exhibited by certain copolymers of a diolefin or an olefin and styrene, the use of such polymers for various pressure sensitive adhesive applications is growing in the industry.
Copolymers made from polystyrene and a diolefin are widely used in the production of adhesives such as, for example, styrene/isoprene/styrene (SIS), styrene/butadiene/styrene (SBS), and styrene/ethylene/butylene/styrene (SEBS), and the like. All of these copolymers whether formed by polymerization of polymer block or by random polymerization, are blended with tackifying resins in order to form the adhesive.
However, when copolymers are mixed with tackifying resins in order to form adhesives, many requirements and factors are important such as the ease with which the resin is blended with the copolymer and the control of the tack as well as the long term properties of the adhesive. Further, the adhesives industry has increased the demand for low softening point resins and market requirements dictate the desirability of resins which are not only liquid, i.e., softening point about 40.degree. C. or less, but that are light in color, even a Gardner color of less than about 3. However, a resin would be considered to be sufficiently light in color for some applications with a Gardner color of 6 or even 7.
Many attempts have been made to prepare resins having these properties for use in the blending with copolymers to form adhesives, but all have fallen short of the mark in one respect or another. While other attempts have been made to prepare light color, low softening point resins such as those described in, for example, U.S. Pat. Nos. 3,963,653; 3,931,125; 3,574,792 and 4,078,132, most attempts have been centered around the preparation of aliphatic resins of the type described, for example, in U.S. Pat. Nos. 3,813,357; 3,692,756; 3,661,870; 3,804,788; 3,853,826; 3,872,064; 3,098,983 and 4,153,771. Unfortunately, aliphatic resins do not provide desired adhesive properties with many copolymers. Other components are required, usually an oil such as a naphthenic oil for example, to impart the tack or other requisite adhesive properties to the adhesive. The presence of the oil itself can cause detrimental adhesive performance. The liquid resins containing aromatic components solve these problems.
Prior attempts to incorporate aromaticity into the resin have generally caused an unacceptable high color level to result, thus making the resulting adhesive unsuitable for various uses.
Accordingly, it is an object of this invention to provide a low softening point hydrocarbon resin; i.e., from 0.degree. C. to about 40.degree. C.
It is a further object of this invention to provide a low softening point resin having a light color while including aromatic substituents to enhance adhesive properties.
Non-aliphatic resins having very low color exist even to the point of being water white. To use these resins to blend with some copolymers to form pressure sensitive adhesives, resins containing some aromaticity and light color, are desired. The presence of an oil plasticizer can cause detrimental results to substrates to which the adhesive is applied. Attempts to incorporate aromaticity, and thus compatibility with the styrene portion of copolymers, into the resin have generally caused an unacceptably high color level making the resulting adhesive unsuitable for various uses.
Accordingly, it is an object of this invention to provide a pressure sensitive adhesive incorporating a low softening point, from 0.degree. C. to about 40.degree. C., and light color aromatic-containing hydrocarbon resin.
It is a further object of this invention to provide adhesives in a binary or tertiary system of a copolymer and a low softening point resin having a light color even while including aromatic substituents to enhance adhesive properties.